原文：http://www.cnblogs.com/ahui/archive/2011/08/04/2127282.html
EF通用的分页实现:
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/// <summary>/// 根据条件分页获得记录/// </summary>/// <param name="where">条件</param>/// <param name="orderBy">排序</param>/// <param name="ascending">是否升序</param>/// <param name="pageIndex">当前页码</param>/// <param name="pageSize">每页大小</param>/// <param name="totalRecord">总记录数</param>/// <returns>记录列表</returns>public virtual List<T> GetMany(Expression<Func<T, bool>> where, string orderBy, bool ascending, int pageIndex, int pageSize, out int totalRecord){ totalRecord = 0; where = where.And(u => u.Flag != (int)Flags.Delete); var list = dbset.Where(where); totalRecord = list.Count(); if (totalRecord <= 0) return new List<T>(); list = list.OrderBy(orderBy, ascending).Skip((pageIndex - 1) * pageSize).Take(pageSize); return list.ToList();} |
动态排序扩展:
public static IQueryable<T> OrderBy<T>(this IQueryable<T> source, string propertyName, bool ascending) where T : class{ Type type = typeof(T); PropertyInfo property = type.GetProperty(propertyName); if (property == null) throw new ArgumentException("propertyName", "Not Exist"); ParameterExpression param = Expression.Parameter(type, "p"); Expression propertyAccessExpression = Expression.MakeMemberAccess(param, property); LambdaExpression orderByExpression = Expression.Lambda(propertyAccessExpression, param); string methodName = ascending ? "OrderBy" : "OrderByDescending"; MethodCallExpression resultExp = Expression.Call(typeof(Queryable), methodName, new Type[] { type, property.PropertyType }, source.Expression, Expression.Quote(orderByExpression)); return source.Provider.CreateQuery<T>(resultExp);} |
如果要通过Expression获取字段，可以使用以下代码:
/// <summary>/// 获取对应的字段名/// </summary>/// <typeparam name="TSource"></typeparam>/// <param name="keySelector"></param>/// <returns></returns>public static string GetMemberName<TSource, TKey>(Expression<Func<TSource, TKey>> keySelector){ string fieldName = null; var exp = keySelector.Body as UnaryExpression; if (exp == null) { var body = keySelector.Body as MemberExpression; fieldName = body.Member.Name; } else { fieldName = (exp.Operand as MemberExpression).Member.Name; } return fieldName;} |
多条件组合(参见老赵相关文章):
/// <summary>/// 统一ParameterExpression/// </summary>internal class ParameterReplacer : ExpressionVisitor{ public ParameterReplacer(ParameterExpression paramExpr) { this.ParameterExpression = paramExpr; } public ParameterExpression ParameterExpression { get; private set; } public Expression Replace(Expression expr) { return this.Visit(expr); } protected override Expression VisitParameter(ParameterExpression p) { return this.ParameterExpression; }}public static class PredicateExtensionses{ public static Expression<Func<T, bool>> True<T>() { return f => true; } public static Expression<Func<T, bool>> False<T>() { return f => false; } public static Expression<Func<T, bool>> And<T>(this Expression<Func<T, bool>> exp_left, Expression<Func<T, bool>> exp_right) { var candidateExpr = Expression.Parameter(typeof(T), "candidate"); var parameterReplacer = new ParameterReplacer(candidateExpr); var left = parameterReplacer.Replace(exp_left.Body); var right = parameterReplacer.Replace(exp_right.Body); var body = Expression.And(left, right); return Expression.Lambda<Func<T, bool>>(body, candidateExpr); } public static Expression<Func<T, bool>> Or<T>(this Expression<Func<T, bool>> exp_left, Expression<Func<T, bool>> exp_right) { var candidateExpr = Expression.Parameter(typeof(T), "candidate"); var parameterReplacer = new ParameterReplacer(candidateExpr); var left = parameterReplacer.Replace(exp_left.Body); var right = parameterReplacer.Replace(exp_right.Body); var body = Expression.Or(left, right); return Expression.Lambda<Func<T, bool>>(body, candidateExpr); }} |
调用示例:
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public static PagedList<UsersDTO> GetUsers(int pageIndex, int pageSize, string orderBy, bool ascending, Companys company, string email, string nickName, bool? isAdmin, UserStatus userStatus){ PagedList<UsersDTO> result = new PagedList<UsersDTO>(pageIndex, pageSize); int totalRecord = 0; Expression<Func<Users, bool>> where = PredicateExtensionses.True<Users>(); if (company != Companys.All) where = where.And(u => u.Company == (int)company); if (!string.IsNullOrEmpty(email)) where = where.And(u => u.Email.Contains(email)); if (!string.IsNullOrEmpty(nickName)) where = where.And(u => u.NickName.Contains(nickName)); if (isAdmin.HasValue) { if (isAdmin.Value) where = where.And(u => u.IsAdmin == 1); else where = where.And(u => u.IsAdmin == 0); } if (userStatus != UserStatus.All) where = where.And(u => u.UserStatus == (int)userStatus); if (string.IsNullOrEmpty(orderBy)) orderBy = MapHelper.GetMappedName<UsersDTO, Users>(u => u.UserId); else orderBy = MapHelper.GetMappedName<UsersDTO, Users>(orderBy); List<Users> list = _usersDao.GetMany(where, orderBy, ascending, pageIndex, pageSize, out totalRecord); result.TotalRecordCount = totalRecord; foreach (var data in list) { result.Items.Add(Mapper.Map<Users, UsersDTO>(data)); } return result;} |
上述方法的缺点是无法针对2个字段一起排序，不过只要修改排序参数还是可以实现的！
另外这种分页查询只能针对一个表或者视图